Lost foam casting of products is well known in the casting industry. However, the lost foam casting process sometimes results in surface porosities on cast parts. Surface porosity defects are also present in sand casting, die casting and permanent mold casting processes. This porosity causes failures for many parts, particularly for parts that require sealing on a surface containing such porosity, because the porosity causes leaks around the seals. As a result, many cast products are rejected and scrapped for quality considerations.
Surprisingly, it has been found that the surface porosity problem may be remedied by a highly efficient restoration process that eliminates surface porosity on an exposed surface. The restoration process of the present application allows for the restoration of parts that would otherwise be scrapped creating a strong economic advantage. The process of the present application is also superior to the restoration processes that currently defines the state of the art.
In the current state of the art, surface porosity repair is achieved through the use of polymer matrix repair putty such as Devcon®, or the like. This approach to the repair of surface porosities is termed the “putty solution.” The disadvantage of the use of polymer matrix repair putty is that it may not be used on surface porosity smaller than 0.080 inches in diameter. As proper O-ring sealing requires elimination of surface porosities as small as 0.010 inches in diameter, the putty solution is an imperfect restoration process.
In order to remedy the deficiencies in the putty solution, surface porosities between 0.010 inches and 0.080 inches are drilled out so that they reach the 0.080 inch requirement and are subsequently filled with the polymer matrix repair putty. Still, the solution is imperfect as the drilling increases the surface porosity before the Devcon® repair putty is able to effectively fill the porosity with a sufficient bonding patch. The drilling step also requires the use of additional resources making the process less efficient. Additionally, the patch is not aesthetically pleasing to consumers and may convey a message that the blocks are substandard. Further, although long term life of polymer matrix repair putty patches themselves are presumed acceptable, it does decrease heat transfer locally and the long term interaction with the aluminum interfaces are in question.
Another drawback of the putty solution is that manufacturing restrictions only allow three polymer matrix repair putty patches per engine block. The putty solution further complicates plant productivity efficiencies insofar as the putty requires curing for 24 hours before final finishing of the engine block surface. Therefore, a combination of the high pressure die cast process along with the putty solution requires a significant queue for an engine block line that requires continuous seven day production to keep up with a five day demand.
An additional secondary operation utilized in the current state of the art is the use of a metal soldering patch in replacement of the polymer matrix repair putty. This “soldering solution” requires the application of a low melting point alloy on top of the identified surface porosity. Conceptually, this solution has three main advantages: 1) the patch would not be visible after cleanup; 2) it could be utilized on more than three repair sites per engine block head deck; and 3) it would not require any curing time between application and finishing, thus eliminating the need for a queue of blocks.
However, the soldering solution has a major drawback in that a Galvanic couple exists between the dissimilar base metal and soldering patch. The Galvanic couple is problematic when it comes into contact with salt water, because salt water corrodes the soldering patch. As many of the products produced by the Applicant are for marine applications, and specifically for salt water marine applications, such a problem is quite disadvantageous. Further, the soldering solution requires a heat input to the engine block surface which may result in heat distortion defects, discoloration, and overaging of the precipitation strengthened cast product.
As a result of the concerns about the putty solution as well as the soldering solution, alternative solutions have been explored. Surprisingly, the restoration process of the present application captures the three noted advantages of the soldering solution without having a bonding problem, a Galvanic corrosion problem, nor a heat input problem. This novel restoration process efficiently and economically restores for use cast part surfaces having surface porosity defects. The restoration process of the present application eliminates surface porosity defects using a spray filler. In one embodiment, the spray filler is significantly different in composition from the substrate material. In other embodiments, the filler and substrate material are the same or similar. Further, with the present application, there is no need to make smaller porosity defects “bigger” for applying the repair spray nor is there a limit to the number or size of porosity defects that may be repaired. Further, there is no heat distortion imparted to the engine blocks nor do Galvonic corrosion concerns exist.
As a result of these advantages, there is significantly less scrapping of cast products, resulting in a much more efficient production process. The restoration process of the present application also does not require any waiting or curing time between the application of the restoration process and the final finishing of the block. Thus, no production queue is needed and level loading of the blocks may be planned through the production and machining process, further increasing the efficiency of production compared to the putty solution or the soldering solution. Finally, the aesthetic problem associated with the putty solution is eliminated as repaired porosity defects are not visible after clean up.
Metal spraying of ceramic materials for wear resistance has been commercialized in the enhancement of crank pin journals, as well as in metal spraying of complete cylinder bores. However, neither of the above stated uses of metal spraying have been contemplated for the restoration of surface porosity defects.
Crank pin journals are defined as the area where a connecting rod attaches to a crankshaft in an engine. The use of metal spray enhances the durability of crank pen journals to wear by building up the area of attachment. Similarly, the aircraft industry has used metal spraying of complete cylinder bores to produce a coating that reduces wear problems.
With the metal spraying being utilized to create a wear surface, the noted processes require a large capitalized systems approach. This is significantly different from the restoration of miniscule surface porosity defects to allow the use of the high pressure die casting process. Further, the process of the current invention is also quite different from any “rapid prototyping” process that builds entire articles, for the same reasons already cited. The use of this micro-area, restoration process to add value to the high pressure die cast process therefore is a new and significantly useful addition to the state of the art.
Accordingly, the present application provides a restoration process for repairing surface porosity defects in a cast component. The process comprises the steps of: identifying an area on a component surface containing at least one porosity defect resulting from the casting process, the area defining a restoration area; applying a restoration spray to the restoration area; and finishing the restoration area. In one embodiment, the component surface and the restoration spray comprise distinct compositions. For example, the component surface may comprise a metallic substrate and the restoration spray may comprise a separate, distinct metallic filler. As a further example, the component surface may comprise a metallic substrate and the restoration spray may comprise a polymeric filler. As a further example, the component surface may comprise a polymeric substrate, and the restoration spray may comprise a metallic filler. By way of further example, the component surface may comprise a polymeric substrate, and the restoration spray comprise a different polymeric filler. By way of further example, the component surface may be a cast iron surface, and the restoration spray may comprise a nickel alloy. The cast component may be cast utilizing a lost foam casting process, a sand casting process, a die casting process or a permanent mold casting process. In one embodiment, the step of applying the restoration spray comprises applying the spray with a spray gun. In another embodiment, the step of finishing the restoration area further comprises removing excess restoration spray material.
The present application also contemplates a restoration process for preparing surface porosity defects on a sealing surface requiring a zero porosity tolerance. The process comprises the steps of identifying an area on a sealing surface containing at least one porosity defect, this area defining a restoration area; applying a restoration spray to the restoration area; and finishing the restoration area. In one embodiment, the sealing surface comprises a metallic substrate and the restoration spray comprises a separate, distinct metallic filler. In another embodiment, the sealing surface comprises a metallic substrate and the restoration spray comprises a polymeric filler. In another embodiment, the sealing surface comprises a polymeric substrate and the restoration spray comprises a polymeric filler. In yet another embodiment, the sealing surface comprises a polymeric substrate and the restoration spray comprises a metallic filler. In one example of this process, the sealing surface is cast iron and the restoration spray comprises a nickel alloy filler. The step of finishing the restoration area, in one embodiment, further comprises a moving access restoration spray material. In yet another embodiment, the process inflates a sealing surface that is a mating surface requiring use of a gasket.